Electrode for electrolytic processing

ABSTRACT

An electrode for electrolytic processing has a conductive material and an organic compound having an ion exchange group. The organic compound is chemically bonded to a surface of the conductive material. The organic compound comprises thiol or disulfide. The ion exchange group comprises at least one of a sulfo group, a carboxyl group, a quaternary ammonium group, and an amino group. The conductive material includes at least one of gold, silver, platinum, copper, gallium arsenide, cadmium sulfide, and indium oxide (III).

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of International Application No.PCT/JP03/12650, filed Oct. 2, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode for electrolyticprocessing, and more particularly to an electrode to be used as aprocessing electrode to process a substrate and/or a feeding electrodeto feed the substrate during an electrolytic process using a fluid,particularly pure water. The present invention also relates to anelectrolytic processing apparatus and method using such an electrode.The present invention also relates to a method of promoting todissociate liquid into ions, and more particularly to a method ofpromoting dissociation of liquid into ions during an electrolyticprocess.

2. Description of the Related Art

In recent years, there has been a growing tendency to replace aluminumor aluminum alloy as a metallic material for forming interconnectioncircuits on a substrate such as a semiconductor wafer with copper (Cu)having a low electric resistivity and a high electromigrationresistance. Copper interconnections are generally formed by fillingcopper into fine recesses formed in a surface of a substrate. As methodsfor forming copper interconnections, there have been employed chemicalvapor deposition (CVD), sputtering, and plating. In any of the methods,after a copper film is formed on substantially the entire surface of asubstrate, unnecessary copper is removed by chemical mechanicalpolishing (CMP).

FIGS. 1A through 1C show an example of a process of forming a copperinterconnection in a substrate W. As shown in FIG 1A, an insulating film2, such as an oxide film of SiO₂ or a film of low-k material, isdeposited on a conductive layer 1 a on a semiconductor base 1 on whichsemiconductor devices have been formed. A contact hole 3 and aninterconnection groove 4 are formed in the insulating film 2 bylithography etching technology. Then, a barrier layer 5 made of TaN orthe like is formed on the insulating film 2, and a seed layer 7, whichis used as a feeding layer for electrolytic plating, is formed on thebarrier layer 5 by sputtering, CVD, or the like.

Subsequently, as shown in FIG. 1B, a surface of the substrate W isplated with copper to fill the contact hole 3 and the interconnectiongroove 4 with copper and to form a copper film 6 on the insulating film2. Thereafter, the surface of the substrate W is polished by chemicalmechanical polishing (CMP) to remove the copper film 6 on the insulatingfilm 2 so that the surface of the copper film 6 filled in the contacthole 3 and the interconnection groove 4 is made substantially even withthe surface of the insulating film 2. Thus, as shown in FIG. 1C, aninterconnection comprising the copper film 6 is formed in the insulatinglayer 2.

Recently, components in various types of equipment have become finer andhave required higher accuracy. As submicronic manufacturing technologyhas commonly been used, the properties of the materials are greatlyinfluenced by the machining method. Under these circumstances, in aconventional mechanical machining method in which a desired portion in aworkpiece is physically destroyed and removed from a surface thereof bya tool, a large number of defects may be produced by the machining, thusdeteriorating the properties of the workpiece. Therefore, it isimportant to perform machining without deteriorating the properties ofmaterials.

Some processing methods, such as chemical polishing, electrochemicalmachining, and electrolytic polishing, have been developed in order tosolve the above problem. In contrast to the conventional physicalmachining methods, these methods perform removal processing or the likethrough a chemical dissolution reaction. Therefore, these methods do notsuffer from defects such as formation of an altered layer anddislocation due to plastic deformation, so that processing can beperformed without deteriorating the properties of the materials.

In an electrochemical machining process, particularly in anelectrochemical machining process using pure water or ultrapure water,an ion exchanger such as an ion exchange membrane or an ion exchangefiber is employed to increase the processing rate. Pure water refers towater having a resistivity of 0.1 MΩ·cm or more at 25° C., and ultrapurewater refers to water having a resistivity of 10 MΩ·cm or more at 25° C.Ion exchangers generally comprise an ion exchange resin or an ionexchange membrane in which an ion exchange group, such as a sulfo group,a carboxyl group, a quaternary ammonium group (═N⁺═), or a tertiary orlower amino group, is bonded to a base material, such as a copolymer ofstyrene and divinylbenzene, or a fluororesin. Further, there has beenknown an ion exchange fiber in which an ion exchange group is introducedinto nonwoven fabric by graft polymerization.

FIG. 2 is a schematic diagram showing an electrolytic processingapparatus using conventional ion exchangers. As shown in FIG. 2, theelectrolytic processing apparatus has a power supply 800, an anode(electrode) 810 connected to the power supply 800, and a cathode(electrode) 820 connected to the power supply 800. The anode 810 has anion exchanger 830 attached to a surface thereof, and the cathode 820 hasan ion exchanger 840 attached to a surface thereof. A fluid 860 such aspure water or ultrapure water is supplied between the electrodes 810,820 and a workpiece 850 (e.g., a copper film). Then, the workpiece 850is brought into contact with or close to the ion exchangers 830, 840attached to the surfaces of the electrodes 810, 820. A voltage isapplied between the anode 810 and the cathode 820 by the power supply800. Water molecules in the fluid 860 are dissociated into hydroxideions and hydrogen ions by the ion exchangers 830, 840. For example, theproduced hydroxide ions are supplied to a surface of the workpiece 850.The concentration of the hydroxide ions is thus increased near theworkpiece 850, and atoms in the workpiece 850 and the hydroxide ions arereacted with each other to perform removal of a surface layer of theworkpiece 850. Thus, the ion exchangers 830, 840 are considered to havecatalysis for decomposing water molecules in the fluid 860 intohydroxide ions and hydrogen ions.

However, with respect to the conventional ion exchange resin or ionexchange fiber, when the electrodes 810 and 820 have a small size (i.e.,a small diameter), the ion exchangers 830 and 840 cannot be disposedseparately on the surfaces of these electrodes 810 and 820. Therefore,the anode 810 and the cathode 820 have to be covered with an ionexchanger extending over both of the anode 810 and the cathode 820.

In such a case, if the distance L₁ between the anode 810 and the cathode820 is smaller than the distance L₂ between the electrodes 810, 820 andmetal (e.g., copper) as the workpiece 850, then an electric currentflows between the electrodes 810 and 820 more than between theelectrodes 810, 820 and the workpiece 850. Therefore, the distance L₁between the electrodes 810 and 820 should be set to be larger than thedistance L₂ between the electrodes 810, 820 and the workpiece 850.

However, the thicknesses of the ion exchangers 830, 840 prevent thedistance L₂ between the electrodes 810, 820 and the workpiece 850 frombeing sufficiently reduced. Accordingly, the anode 810 and the cathode820 cannot be disposed as close to each other as would be preferred. Asa result, the anode 810 and the cathode 820 have limitations in theirshapes or the like.

Further, a conventional ion exchange fiber is problematic in that fibersmay be removed from the ion exchanger during an electrolytic process sothat the removed fibers cause variations of processing propertiesaccording to time elapsed. It has been feared that seams of the fibersmay have an influence on the surface roughness of the workpiece. Fromthis point of view, in order to flatten the entire surface of aworkpiece, attempts have been made to wind a meshed ion exchange fiberaround nonwoven fabric and attach it to a cylindrical electrode.However, when an ion exchanger has an uneven thickness, the flatness ofthe surface of the workpiece may be influenced by the uneven thicknessof the ion exchanger.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above drawbacks. Itis, therefore, a first object of the present invention to provide anelectrode for electrolytic processing which can achieve stableprocessing performance and can flexibly cope with small electrodes andvarious shapes of electrodes.

A second object of the present invention is to provide an electrolyticprocessing apparatus and method using such an electrode.

A third object of the present invention is to provide a method ofpromoting to dissociate liquid into ions which can achieve stableprocessing performance.

In order to attain the first object, according to a first aspect of thepresent invention, there is provided an electrode for electrolyticprocessing. The electrode has a conductive material and an organiccompound having an ion exchange group. The organic compound ischemically bonded to a surface of the conductive material.

According to the present invention, an ion exchange material having anion exchange function can be bonded directly to a conductive material.Thus, the conductive material with the ion exchange material can be usedas an electrode for electrolytic processing. With such an arrangement,it is possible to reduce the distance between an electrode and aworkpiece and hence the distance between an electrode serving as ananode and an electrode serving as a cathode. Therefore, the electrodeaccording to the present invention can flexibly cope with smallelectrodes and various shapes of electrodes. Furthermore, because ionexchange materials can be bonded separately to a conductive materialserving as an anode and a conductive material serving as a cathode, aleakage current can be prevented from being produced between the anodeand the cathode.

The organic compound may comprise thiol or disulfide. The ion exchangegroup may comprise at least one of a sulfo group, a carboxyl group, aquaternary ammonium group, and an amino group. The conductive materialmay include at least one of gold, silver, platinum, copper, galliumarsenide, cadmium sulfide, and indium oxide (III).

The conductive material should preferably have meshes because suchmeshes can allow water to pass therethrough to decompose waterefficiently. When a workpiece is brought into contact with the electrodeduring an electrolytic process, scratches may be produced on a surfaceof the workpiece. From this point of view, it is desirable that aworkpiece is not brought into contact with the electrode during anelectrolytic process.

According to a second aspect of the present invention, there is providedan electrode for electrolytic processing. The electrode has a conductivecarbon material and an ionic dissociation functional group. A surface ofthe conductive carbon material is chemically modified by the ionicdissociation functional group.

With such an electrode, the surface of the electrode has catalysis fordecomposing water molecules into ions. Therefore, it is possible toreduce the distance between an electrode and a workpiece and hence thedistance between an electrode serving as an anode and an electrodeserving as a cathode. Therefore, the electrode according to the presentinvention can flexibly cope with small electrodes and various shapes ofelectrodes. Furthermore, because each of an electrode serving as ananode and an electrode serving as a cathode can have catalysis, aleakage current can be prevented from being produced between the anodeand the cathode.

The ionic dissociation functional group may comprise a sulfo group or acarboxyl group. The ionic dissociation functional group may comprise atleast one of a quaternary ammonium group, and a tertiary or lower aminogroup. The conductive carbon material may comprise glassy carbon,fullerene, or carbon nanotubes.

According to a third aspect of the present invention, there is providedan electrode for electrolytic processing. The electrode has a graphiteintercalation compound containing alkali metal.

With such an electrode, water molecules are considered to be decomposedinto ions by alkali metal intercalated between layers of the graphite.Therefore, it is possible to reduce the distance between an electrodeand a workpiece and hence the distance between an electrode serving asan anode and an electrode serving as a cathode. Therefore, the electrodeaccording to the present invention can flexibly cope with smallelectrodes and various shapes of electrodes. Furthermore, because eachof an electrode serving as an anode and an electrode serving as acathode can have catalysis, a leakage current can be prevented frombeing produced between the anode and the cathode.

In order to attain the second object of the present invention, accordingto a fourth aspect of the present invention, there is provided anelectrolytic processing apparatus having a processing electrode and afeeding electrode to feed a workpiece. The electrolytic processingapparatus also has a workpiece holder for holding the workpiece andbringing the workpiece into contact with or close to the processingelectrode. The electrolytic processing apparatus includes a power supplyfor applying a voltage between the processing electrode and the feedingelectrode, and a fluid supply unit for supplying a fluid between theworkpiece and the processing electrode. At least one of the processingelectrode and the feeding electrode employs any one of theaforementioned electrodes.

According to a fifth aspect of the present invention, there is providedan electrolytic processing method. A workpiece is fed through a feedingelectrode. A voltage is applied between the feeding electrode and aprocessing electrode. A fluid is supplied between the workpiece and theprocessing electrode. The workpiece is brought into contact with orclose to the processing electrode. At least one of the processingelectrode and the feeding electrode employs any one of theaforementioned electrodes.

In order to attain the third object of the present invention, accordingto a sixth aspect of the present invention, there is provided a methodof promoting dissociation of liquid into ions by a conductive materialto which an organic compound having an ion exchange group is chemicallybonded.

The organic compound may comprise thiol or disulfide. The ion exchangegroup may comprise at least one of a sulfo group, a carboxyl group, aquaternary ammonium group, and an amino group. The conductive materialmay include at least one of gold, silver, platinum, copper, galliumarsenide, cadmium sulfide, and indium oxide (III).

The above and other objects, features, and advantages of the presentinvention will be apparent from the following description when taken inconjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C are diagrams showing an example of a process offorming a copper interconnection in a substrate;

FIG. 2 is a schematic diagram showing an electrolytic processingapparatus using conventional ion exchangers;

FIG. 3 is a schematic diagram showing an electrolytic processingapparatus using an electrode according to the present invention;

FIGS. 4A and 4B are graphs showing current-voltage properties when anelectrolysis process was performed with use of an electrode having aconductive material and an organic compound having an ion exchange groupchemically bonded to the conductive material;

FIG. 5 is a schematic diagram showing an example of an electrolyticprocessing apparatus using an electrode according to the presentinvention;

FIG. 6 is a vertical cross-sectional view showing a main frame in theelectrolytic processing apparatus shown in FIG. 5;

FIG. 7 is a perspective view showing a holding portion and a processingelectrode in the electrolytic processing apparatus shown in FIG. 6;

FIG. 8 is perspective view showing a holding portion and a processingelectrode in another electrolytic processing apparatus according to thepresent invention;

FIG. 9 is a schematic diagram showing an example of an electrolyticprocessing apparatus schematic another type of electrode according tothe present invention;

FIG. 10 is a graph showing the current-voltage properties of theelectrode shown in FIG. 9;

FIG. 11 is a graph showing the current-voltage properties of theelectrode shown in FIG. 9;

FIG. 12 is a graph showing the current-voltage properties of theelectrode shown in FIG. 9;

FIG. 13 is a schematic diagram showing an example of an electrolyticprocessing apparatus having another type of electrode according to thepresent invention;

FIG. 14 is a schematic diagram showing an experimental device used tomeasure the current-voltage properties of an electrode according to thepresent invention; and

FIG. 15 is a graph showing the current-voltage properties of theelectrode shown in FIG. 13, which are measured by the experimentaldevice shown in FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An electrode and an electrolytic processing apparatus using an electrodeaccording to embodiments of the present invention will be describedbelow with reference to the accompanying drawings. In the followingembodiments, a substrate is used as a workpiece and processed by anelectrolytic processing apparatus. However, the present invention isapplicable to any workpiece other than the substrate.

FIG. 3 is a schematic diagram showing an example of an electrolyticprocessing apparatus using an electrode according to the presentinvention. As shown in FIG. 3, the electrolytic processing apparatus hasa pair of electrodes 1 and 2 for electrolytic processing. The electrodes1 and 2 have conductive materials 1 a and 2 a as base materials,respectively. The conductive materials 1 a and 2 a are connected to ananode and a cathode of a power supply 3, respectively. An organiccompound having an ion exchange group is chemically bonded to a surfaceof the conductive material la to form an ion exchange material 1 b onthe surface of the conductive material 1 a, and an organic compoundhaving an ion exchange group is chemically bonded to a surface of theconductive material 2 a to form an ion exchange material 2 b on thesurface of the conductive material 2 a. A fluid 5 such as pure water orultrapure water is supplied between the electrodes 1, 2 and a workpiece4 (e.g., a copper film formed on a substrate). Then, the workpiece 4 isbrought into contact with or close to the ion exchange materials 1 b and2 b. A voltage is applied between the conductive carbon materials 1 aand 2 a in the electrodes 1, 2 by the power supply 3. Water molecules inthe fluid 5 are dissociated into hydroxide ions and hydrogen ions by theion exchange materials 1 b and 2 b. For example, the produced hydroxideions are supplied to a surface of the workpiece 4. The concentration ofthe hydroxide ions is thus increased near the workpiece 4, and atoms inthe workpiece 4 and the hydroxide ions are reacted with each other toperform removal of a surface layer of the workpiece 4.

According to the present invention, an ion exchange material having anion exchange function can be bonded directly to a conductive material asa base material. Thus, the conductive material with the ion exchangematerial can be used as an electrode for electrolytic processing, asshown in FIG. 3. With such an arrangement, it is possible to reduce thedistance between the electrodes 1, 2 and the workpiece (substrate) 4 andhence the distance between the electrode 1 serving as an anode and theelectrode 2 serving as a cathode. Therefore, the electrolytic processingapparatus can flexibly cope with small electrodes and various shapes ofelectrodes. Furthermore, because ion exchange materials can be bondedseparately to the conductive material la serving as an anode and theconductive material 2 a serving as a cathode, a leakage current can beprevented from being produced between the anode and the cathode, i.e.,between the electrodes 1 and 2.

As described above, each of the electrodes has the ion exchange materialin which an organic compound having an ion exchange group is chemicallybonded to the electrode. The term “bond” means that a material having anion exchange group is bonded to a conductive material by chemical bond,not by an adhesive or the like. In a usual ion exchange resin, amaterial having an ion exchange group is “bonded” to an organic matterincluded in the resin.

It is desirable that the conductive material to which an organiccompound is bonded has meshes, e.g., a lattice pattern or a form of apunching metal, because such meshes can allow water to pass therethroughto decompose water efficiently.

Such an electrode can be produced as follows. There will be described anexample in which sodium 1-propanethiol-3-sulfonate (HSC₃H₆—SO₃Na) wasused as an organic compound having an ion exchange group and was bondeddirectly to a platinum (Pt) substrate to produce an electrode. A sodiumsalt of sulfo group is substituted at the 3-end of 1-propanethiol toform sodium 1-propanethiol-3-sulfonate (thiol).

First, a flat platinum substrate, for example, having a length of 34 mm,a width of 12.5 mm, and a thickness of 0.5 mm, was prepared. An organicmatter on a surface of the platinum substrate was removed by a sulfuricacid and hydrogen peroxide aqueous solution. Then, the platinumsubstrate was immersed in an aqueous solution of sodium1-propanethiol-3-sulfonate, which had a concentration of severalmilimoles/liter, for about 12 hours. Sodium 1-propanethiol-3-sulfonatehas hydrophilicity under the influence of a sulfo group as a functionalgroup. Therefore, while the surface of the platinum substrate washydrophobic before the immersion, the surface of the platinum substratebecame hydrophilic after the immersion so that thiol is bonded to thesurface of the platinum substrate. Thus, a flat platinum electrode(Pt—SC₃H₆—SO₃Na), which has a catalyst (an ion dissociation function),could be produced.

The catalysis in dissolution reactions of water molecules was measuredon the platinum electrode modified by sodium 1-propanethiol-3-sulfonate,which is hereinafter referred to as a thiol platinum electrode.Specifically, a thiol platinum electrode produced as described above wasinstalled into an experimental device having parallel plate electrodes,and electrolysis was performed with ultrapure water. The current-voltageproperties were measured for the following cases. Further, thecurrent-voltage properties were measured for a comparative experiment inwhich normal platinum electrodes were used as an anode and a cathode.

(1) A thiol platinum electrode was used as an anode, and a normalplatinum electrode was used as a cathode.

(2) A normal platinum electrode was used as an anode, and a thiolplatinum electrode was used as a cathode.

A fluororesin sheet was disposed between the electrodes. Areas of theelectrodes facing each other were set to be about 0.4 cm². The distancebetween the electrodes was adjusted by the thickness of the fluororesinsheet. Measurements were conducted under two conditions in which thedistance between the electrodes was 50 μm and 12 μm.

FIG. 4A is a graph showing results of an experiment in which thedistance between the electrodes was 12 μm, and FIG. 4B is a graphshowing results of an experiment in which the distance between theelectrodes was 50 μm. It can be shown from FIGS. 4A and 4B that when athiol platinum electrode was used as an anode or a cathode, theelectrolytic current was increased by several times to several tens oftimes (50 times at maximum) as compared to a case where normal platinumelectrodes were used as an anode and a cathode. Thus, the thiol platinumelectrode served as a catalyst for dissociating water into ions. Aliquid in which the dissociation is promoted is not limited to water.

It can be seen from FIGS. 4A and 4B that an increase of electrolyticcurrent was larger as the distance between the electrodes was smaller.Specifically, when the distance between the electrodes was 12 μm, theelectrolytic current value was about 50 times as large as that in thecase of using the normal platinum electrodes (see FIG. 4A). However,when the distance between the electrodes was 50 μm, the electrolyticcurrent value was about 5 times as large as that the case of using thenormal platinum electrodes (see FIG. 4B).

In the above example, platinum was used as the conductive material towhich the organic compound was bonded. However, the conductive materialis not limited to platinum. For example, metal such as gold, silver, orcopper may be used as the conductive material. Alternatively, theconductive material may comprise a glass substrate having an Au film, orGaAs (gallium arsenide), CdS (cadmium sulfide), In₂O₃ (indium oxide(III)), carbon (graphite), or the like. According to another experiment,it has been confirmed that current-voltage properties similar to theabove could be achieved in the case of using a glass substrate having anAu film. Further, an organic conductive material such as a polyanilinebased material or carbon nanotubes may be used as the conductivematerial. Specifically, an organic compound having an ion exchange groupmay be bonded directly to an organic conductive material.

In the above example, thiol was used as the organic compound to bebonded to the conductive material. However, the organic compound is notlimited to thiol. For example, disulfide or an organic conductivematerial such as a polyaniline based material or carbon nanotubes may beused as the organic compound. Further, the ion exchange group is notlimited to a sulfo group as described above. For example, a carboxylgroup, a quaternary ammonium group, or an amino group may be used as theion exchange group. According to an experiment, it has been confirmedthat effects similar to those described above could be achieved when acarboxyl group was used as an ion exchange group of thiol.

An electrode according to the present invention is applicable to anelectrolytic processing apparatus as shown in FIGS. 5 through 7. FIG. 5is a schematic diagram showing an example of an electrolytic processingapparatus using an electrode according to the present invention, FIG. 6is a vertical cross-sectional view showing a main frame 14 in theelectrolytic processing apparatus shown in FIG. 5, and FIG. 7 is aperspective view showing a main part of the main frame 14 shown in FIG.6.

As shown in FIG. 5, the electrolytic processing apparatus mainlycomprises a main frame 14 having a machining chamber 12 for holdingultrapure water 10 therein, an ultrapure water circulation/purificationdevice 22, and a high-pressure ultrapure water supply unit 28. Theultrapure water circulation/purification device 22 has a waste watertank 16, an ultrapure water circulation/purification section 18, and ahigh-pressure pump 20. The high-pressure ultrapure water supply unit 28has a plunger pump 24 and a pressure transmitter 26. For example, themachining chamber 12 is made of stainless steel.

As shown in FIG. 5, the main frame 14 has a workpiece holder (holdingtable) 30 for detachably holding a workpiece W such as a semiconductorwafer in a horizontal direction by suction. The workpiece holder 30 isdisposed within the machining chamber 12 and has three degrees XYθ offreedom. Specifically, the workpiece W held by the workpiece holder 30is horizontally movable in the directions of X and Y (see FIG. 7) and isrotatable about the θ axis (Z axis) on the horizontal plane while theworkpiece W is immersed in the ultrapure water 10. The workpiece holder30 serves to hold the workpiece W and to supply an electric current tothe workpiece W. For example, the workpiece holder 30 is made oftitanium and has a platinum plated surface of 1 μm in thickness. Theworkpiece holder 30 is supported in radial and thrust directions by ahydrostatic bearing 32 using ultrapure water (see FIG. 5).

As shown in FIG. 7, a columnar or cylindrical processing electrode 34 isdisposed above the workpiece holder 30. The processing electrode 34 hasa shaft center O-O extending horizontally. The processing electrode 34is formed by an electrode according to the present invention.Specifically, an ion exchange material 34 b having an ion exchangefunction is formed on a columnar or cylindrical conductive material 34 ato which an organic compound having an ion exchange group is chemicallybonded. The conductive material 34 a in the processing electrode 34 isconnected to a power supply 38. The ion exchange material 34 b serves asa catalyst for dissociating water molecules in the ultrapure waterbetween the processing electrode 34 and the workpiece W into hydrogenions and hydroxide ions.

The processing electrode 34 is coupled to a vertically movable rotatingshaft 36 extending along the shaft center O-O. Thus, the processingelectrode 34 can be rotated about the shaft center O-O in accordancewith the rotation of the rotating shaft 36. The processing electrode 34can be moved vertically so as to adjust the distance between theprocessing electrode 34 and the workpiece W held by the workpiece holder30. As with the workpiece holder 30, the rotating shaft 36 is supportedin the radial and thrust directions by a hydrostatic bearing (not shown)using ultrapure water. When an electrolytic process is performed, theprocessing electrode 34 is lowered so as to bring a lower end portion ofthe ion exchange material 34 b into contact with or close to a surfaceof the workpiece held by the workpiece holder 30.

The electrolytic processing apparatus has the power supply 38 forapplying a voltage between the processing electrode 34 and the workpieceW held by the workpiece holder 30. In this embodiment, for example, inorder to perform an electrolytic process of copper as the workpiece, theprocessing electrode 34 is connected to a cathode of the power supply38, and workpiece (copper) W is connected to an anode of the powersupply 38. However, depending upon the types of workpieces, theprocessing electrode 34 may be connected to the anode of the powersupply 38, and the workpiece W may be connected to the cathode of thepower supply 38.

As described above, the workpiece holder 30 is rotatable about thevertical axis, and the processing electrode 34 is rotatable about thehorizontal axis. The workpiece holder 30 and the processing electrode 34are respectively rotated in directions such that the ultrapure water 10is revolved. An ultrapure water supply nozzle 40 for supplying ultrapurewater at a high pressure between the workpiece W held by the workpieceholder 30 and the processing electrode 34 is disposed at the upstreamside of the directions of the rotation. While at least one of theprocessing electrode 34 and the workpiece W is being rotated, theultrapure water 10 is supplied between the processing electrode 34 andthe workpiece W from the upstream side of the directions of the rotationto effectively remove bubbles or machining products which would remainbetween the processing electrode 34 and the workpiece W.

As shown in FIG. 5, ultrapure water is purified by the ultrapure watercirculation/purification section 18 in the ultrapure watercirculation/purification device 22, pressurized by the pressuretransmitter 26 in the high-pressure ultrapure water supply unit 28, andsupplied into the ultrapure water supply nozzle 40 by the plunger pump24. Further, as shown in FIG. 5, the ultrapure water 10 held in themachining chamber 12 overflows so as to be stored in the waste watertank 16. Then, the ultrapure water is purified in the ultrapure watercirculation/purification device 22 and returned to the machining chamber12 by the high-pressure pump 20. A portion of the ultrapure water 10 issupplied to the hydrostatic bearing 32.

With the electrolytic processing apparatus thus constructed, theworkpiece W is held by the workpiece holder 30, and the processingelectrode 34 is lowered so as to bring the ion exchange material 34 b ofthe processing electrode 34 into line contact with or close to a surfaceof the workpiece W. In this state, ultrapure water 10 within themachining chamber 12 is purified by the ultrapure watercirculation/purification device 22 and circulated. The processingelectrode 34 is connected to the cathode of the power supply 38, and theworkpiece W is connected to the anode of the power supply 38, so that avoltage is applied between the processing electrode 34 and the workpieceW. At that time, the workpiece holder 30 and the processing electrode 34are simultaneously rotated in directions such that the ultrapure water10 is revolved. The ultrapure water is supplied between the processingelectrode 34 and the workpiece W at a high pressure from the ultrapurewater supply nozzle 40 disposed at the upstream side of the directionsof the rotation. Hydrogen ions and hydroxide ions are produced by achemical reaction occurring on a solid surface of the ion exchangematerial (catalyst) 34 b to perform removal of the surface of theworkpiece W. In this case, a flow of the ultrapure water 10 is formed inthe machining chamber 12 and passed through the ion exchange material 34b to produce a large amount of hydrogen ions and hydroxide ions. Thus, alarge amount of hydrogen ions or hydroxide ions are supplied onto thesurface of the workpiece W to efficiently perform the electrolyticprocess.

As described above, the workpiece holder 30 and the processing electrode34 are simultaneously rotated in directions such that the ultrapurewater 10 is revolved. The ultrapure water is supplied between theprocessing electrode 34 and the workpiece W at a high pressure from theultrapure water supply nozzle 40 disposed at the upstream side of thedirections of the rotation. Accordingly, the ultrapure water 10 presentbetween the workpiece W and the processing electrode 34 can effectivelybe replaced with new ultrapure water, so that gas and machining productsproduced upon the electrolytic process can efficiently be removed torealize a stable electrolytic process.

An electrode according to the present invention is also applicable to anelectrolytic processing apparatus as shown in FIG. 8. The electrolyticprocessing apparatus shown in FIG. 8 differs from the electrolyticprocessing apparatus shown in FIG. 7 in that a processing electrode 134is ellipsoidal or spherical. When the processing electrode 134 islowered, a lower end portion of an ion exchange material 134 b on anouter surface of a conductive material 134 a is brought into pointcontact with the workpiece W held by the workpiece holder 30. In thisstate, the processing electrode 134 and the workpiece holder 30 aresimultaneously rotated. The other structures are the same as thestructures of the electrolytic processing apparatus shown in FIG. 7.

With this electrolytic processing apparatus, since the area of theprocessing portion is reduced, the ultrapure water 10 can easily besupplied to a portion around the processing portion. Accordingly, theelectrolytic process can be performed under stable conditions. Ultrapurewater may not be necessarily ejected from the ultrapure water supplynozzle 40. For example, instead of ejecting ultrapure water, theelectrolytic processing apparatus may employ a tank which holdsultrapure water therein and immerses an electrode and a workpiece in theultrapure water.

Since any chemical material, including abrasive particles and densechemical liquids, other than ultrapure water is not used in theelectrolytic processing apparatus, the machining chamber 14 may becontaminated only by reaction products produced during electrochemicalprocessing. Thus, it is possible to simplify or dispense with a cleaningprocess of a substrate after the electrolytic process. Circulation ofthe ultrapure water can reduce the amount of wastewater. Further, sinceit is not necessary to treat any chemical liquids, operating cost canremarkably be reduced.

In the above embodiments, an organic compound having an ion exchangegroup is chemically bonded to a surface of an electrode to form an ionexchanger on the surface of the electrode. Specifically, gold, silver,platinum, copper, indium oxide, or the like is used as an electrodematerial (conductive material), and thiol, disulfide, or the like isused as an organic compound having an ion exchange group. Such anorganic compound is chemically bonded to the electrode material tointroduce the ion exchange group into the electrode material. Instead ofusing such an electrode, a surface of a conductive carbon material maybe chemically modified by an ionic dissociation functional group.Specifically, a conductive carbon material is used as an electrodematerial, and an ionic dissociation functional group is effectivelyintroduced directly into a surface of the carbon of the conductivecarbon material by inorganic reactions. In such a case, bondings havingno carbon chains due to an organic compound can be produced between theelectrode material and the ionic dissociation functional group (or anion exchange group). Therefore, the thickness of the chemicalmodification layer can be reduced, and the durability (or the resistanceto removal) and the conductivity of the ionic dissociation functionalgroup can be improved.

FIG. 9 is a schematic diagram showing an electrolytic processingapparatus using such an electrode. As shown in FIG. 9, the electrolyticprocessing apparatus has a pair of electrodes 201 and 202. Theelectrodes 201 and 202 have conductive carbon materials 201 a and 202 aconnected to an anode and a cathode of a power supply 203, respectively.A surface of the conductive carbon material 201 a is chemically modifiedwith an ionic dissociation functional group 201 b, and a surface of theconductive carbon material 202 a is chemically modified with an ionicdissociation functional group 202 b. A fluid 205 such as pure water orultrapure water is supplied between the electrodes 201, 202 and aworkpiece 204 (e.g., a copper film formed on a substrate). Then, theworkpiece 204 is brought close to the ionic dissociation functionalgroups 201 b, 202 b in the electrodes 201, 202. A voltage is appliedbetween the conductive carbon materials 201 a and 202 a in theelectrodes 201, 202 by the power supply 203. Water molecules in thefluid 205 are dissociated into hydroxide ions and hydrogen ions by theionic dissociation functional groups 201 b, 202 b. For example, theproduced hydroxide ions are supplied to a surface of the workpiece 204.The concentration of the hydroxide ions is thus increased near theworkpiece 204, and atoms in the workpiece 204 and the hydroxide ions arereacted with each other to perform removal of a surface layer of theworkpiece 204.

Thus, it is possible to reduce the distance between the electrodes 201,202 and the workpiece (substrate) 204 and hence the distance between theelectrode 201 serving as an anode and the electrode 202 serving as acathode. Therefore, the electrolytic processing apparatus can flexiblycope with small electrodes and various shapes of electrodes.Furthermore, because the conductive carbon material 201 a serving as ananode and the conductive carbon material 202 a serving as a cathode areseparately bonded to (or chemically modified by) the ionic dissociationfunctional groups 201 b, 202 b, a leakage current can be prevented frombeing produced between the cathode and the anode, i.e., between theelectrodes 201 and 202.

Such an electrode, which has a conductive carbon material and an ionicdissociation functional group chemically modifying a surface of theconductive carbon material, can be used in an electrolytic processingapparatus of the above embodiments shown in FIGS. 5 through 8, insteadof an electrode in which an organic compound is chemically bonded to asurface of a conductive material.

The ionic dissociation functional group, which chemically modifies thesurface of the conductive carbon material, comprises at least one kindof basic groups selected from a quaternary ammonium group and tertiaryand lower amino groups, or an acidic group such as a sulfo group or acarboxyl group.

When the electrode is to be used to process a relatively large area ofabout 1 cm² or more, the conductive carbon material should preferablycomprise a carbon material that has a flat and smooth surface and can beprocessed in shape with high accuracy, such as glassy carbon. When theelectrode is to be used to perform fine processing at a level of 1 μm orless than 1 μm, fullerene or nanomolecules such as carbon nanotubesshould preferably be used as the conductive carbon material. It isdesirable that the conductive carbon material has meshes because suchmeshes can allow water to pass therethrough to decompose waterefficiently.

Methods of chemically modifying a conductive carbon material with anionic dissociation functional group such as an ion exchange groupinclude immersing a conductive carbon material in a chemical liquid,electrical discharge processing a conductive carbon material in agaseous phase, anodizing a conductive carbon material in an electrolyticsolution, and modifying a conductive carbon material by graftpolymerization.

For example, as a method of immersing a conductive carbon material in achemical liquid, a conductive carbon material is immersed in anoxidizing solution such as a nitric acid. With this method, a surface ofthe conductive carbon material can be readily chemically modified by anionic dissociation functional group such as a carboxyl group. When aconductive carbon material is immersed in heated sulfuric acid, asurface of the conductive carbon material can be chemically modified byan ionic dissociation functional group such as a sulfo group. Further, aconductive carbon material may be immersed in a mixture of concentratedsulfuric acid and concentrated nitric acid to nitride the conductivecarbon material, and then tin and the nitrided conductive carbonmaterial may be immersed in, for example, hydrochloric acid. In thiscase, the conductive carbon material can be chemically modified by anionic dissociation functional group such as an amino group.

For example, as a method of electrical discharge processing a conductivecarbon material in a gaseous phase, plasma is formed in a gas containingoxygen by RF electrical discharge (13.25 MHz), and a conductive carbonmaterial is exposed to the plasma. With this method, a surface of theconductive carbon material can be chemically modified by an ionicdissociation functional group such as a carboxyl group. Plasma may beformed in a nitrogen atmosphere by electrical discharge, and aconductive carbon material may be exposed to the plasma. In such a case,an ionic dissociation functional group having basicity can be introducedinto the conductive carbon material. These methods can suitably be usedto chemically modify a conductive carbon material by an ionicdissociation functional group. See S. S. Wong, A. T. Woolley, E.Joselevich, C. M. Leiber, Chem. Phys. Lett., 306 (1999) 219.

In a method of anodizing a conductive carbon material in an electrolyticsolution, a conductive carbon material is usually used as an anode.Metal such as platinum (Pt), gold (Au), lead (Pb), and zinc (Zn), andany carbon material can be used as a cathode. See J. H. Wandass, J. A.Gardella, N. L. Weinberg, M. E. Bolster, L. Salvati, J. Electrochem.Soc., 134 (1987) 2734. The electrolytic solution may contain nitricacid, sulfuric acid, phosphoric acid, hydrochloric acid, hydrobromicacid, or salts having ions contained in these acids. Such salts includesalts of alkali metal such as lithium, sodium, and potassium, salts ofalkaline-earth metal such as magnesium, calcium, and barium, ammoniumsalt, sulfonium salt, phosphonium salt, and salts of Fe, Cu, andlanthanoide metal. Practically, a single electrolytic solution or amixture of these kinds of electrolytic solutions is used. Although it isdesirable that the electrolytic current density is in a range of fromabout 1 to about 100 mA/cm², the method is not limited to theseconditions. With this method, a surface of a carbon material ischemically modified by a carboxyl group.

In a method of modifying a conductive carbon material by graftpolymerization, for example, graft chains are introduced into aconductive carbon material by a radiation-induced graft polymerization,which comprises a gamma irradiation and a graft polymerization. Then,the introduced graft chains are aminated to introduce a quaternaryammonium group. The capacity of an introduced ion exchange group isdetermined according to the amount of graft chains introduced. The graftpolymerization may be conducted by the use of a monomer such as acrylicacid, styrene, glicidyl methacrylate, sodium styrenesulfonate, orchloromethylstyrene. The amount of the graft chains can be controlled byadjusting the monomer concentration, the reaction temperature, and thereaction time. Further, the introduced graft chains may be treated withheated sulfuric acid to introduce a sulfo group or treated with heatedphosphoric acid to introduce a phosphate group. In the graftpolymerization, a radioactive ray (γ-ray, electron beam, or ultravioletray) may be applied to a base material for pre-irradiation to generate aradical so that the radical reacts with a monomer. Alternatively, a basematerial may be impregnated with a monomer and irradiated with aradioactive ray (γ-ray, electron beam, or ultraviolet ray) forsimultaneous irradiation to perform a radical polymerization.

According to the method of electrical discharge processing a conductivecarbon material in a gaseous phase, an electrode in which a carboxylgroup was introduced into a conductive carbon material was produced asfollows. Two rod-like electrodes, which were moistened with water, werespaced at about 3 cm. An alternating voltage of 100 V was appliedbetween the electrodes. A carbon rod (conductive carbon material), whichwas moistened with water, was inserted into between electrodes. Arcdischarge was caused in an atmosphere to treat a surface of the carbonrod by the arc discharge so as to introduce a carboxyl group into thesurface of the carbon rod (conductive carbon material). The carbon rodwas made of graphite having a diameter of 6 mm. Each end of the carbonrod was rounded. The water used was ultrapure water, which had aresistivity of 18.2 MΩ·cm.

The current-voltage properties were measured in an experimental devicein which the carbon rod thus treated was used as an anode, and aplatinum plate was used as a cathode. The experimental device had anacrylic container holding ultrapure water therein, which has aresistivity of 18.2 MΩ·cm. The carbon rod and the platinum plate facedeach other in the container. After the distance between the carbon rodand the platinum plate was adjusted by a micrometer, a voltage wasapplied between the carbon rod and the platinum plate while ultrapurewater was supplied between the carbon rod and the platinum plate. Atthat time, a flowing current was measured. The distance between thecarbon rod and the platinum plate was set to be 15 μm.

Further, the current-voltage properties were measured in a mannersimilar to the above for a comparative experiment in which a carbon rodbefore the surface treatment by the arc discharge was used as an anode,and a platinum plate was used as a cathode.

FIG. 10 shows results of the above experiments. It can be seen from FIG.10 that the carbon rod into which a carboxyl group was introduced by thesurface treatment with the arc discharge had increased current at 60 Vby ten or more times as compared to the carbon rod into which thecarboxyl group was not introduced.

According to the method of anodizing a conductive carbon material in anelectrolytic solution, an electrode in which a carboxyl group wasintroduced into a conductive carbon material was produced as follows. Acarbon rod (conductive carbon material) was used as an anode andanodized in an H₂SO₄ solution of 20 weight % at a current density of12.5 mA/cm² for 30 minutes. A platinum plate (Pt) was used as a facingelectrode. The carbon rod was made of graphite having a diameter of 6mm. Each end of the carbon rod was rounded. The current-voltageproperties of the anodized carbon rod were measured under conditionssimilar to the above example. The distance between the carbon rod andthe platinum plate was set to be 15 μm.

Further, the current-voltage properties were measured in a mannersimilar to the above example for a comparative experiment in which acarbon rod before the surface treatment by anodization was used as ananode, and a platinum plate was used as a cathode.

FIG. 11 shows results of the above experiments. It can be seen from FIG.11 that the carbon rod into which a carboxyl group was introduced byanodization had increased current by ten or more times as compared tothe carbon rod into which the carboxyl group was not introduced.

The carbon rod into which a carboxyl group was introduced by anodizationwas used as a processing electrode to perform an electrolytic process ofa copper film formed on a silicon substrate. The electrolytic processwas conducted at a voltage of 60 V and a current of 1.07 mA for 10seconds while the distance between electrodes was 25 μm. As a result ofthe electrolytic process, the maximum processed depth was 144 nm. Atthat time, the current efficiency was about 48%. The current efficiencyrefers to a ratio of the quantity of electricity used to process thecopper film to the entire quantity of electricity passed. The currentefficiency was calculated on the assumption that copper was eluted asbivalent ions or bivalent ionic compounds.

The carbon rod into which a carboxyl group was not introduced byanodization was used as a processing electrode to perform anelectrolytic process of a copper film formed on a silicon substrate. Theelectrolytic process was conducted at a voltage of 60 V and a current of0.043 mA for 60 seconds. As a result of the electrolytic process, themaximum processed depth was 12 nm. At that time, the current efficiencywas about 3.3%.

Thus, it can be seen that the carbon rod into which a carboxyl group wasintroduced by anodization had increased current during the electrolyticprocess and increased current efficiency as compared to the carbon rodinto which the carboxyl group was not introduced.

Instead of using an electrode in which a surface of a conductive carbonmaterial is chemically modified by an ion dissociation functional group,a graphite intercalation compound containing alkali metal may be used asan electrode. It is generally desirable that high orientated pyrolyticgraphite (HOPG) is used as graphite (carbon material) in the graphiteintercalation compound. However, when sodium is intercalated as alkalimetal between layers of the graphite, it is desirable that loworientated graphite is used as the graphite in the graphiteintercalation compound. The graphite intercalation compound shouldpreferably have meshes because such meshes can allow water to passtherethrough to decompose water efficiently.

According to the method of immersing a conductive carbon material in achemical liquid, an electrode in which a sulfo group was introduced intoa conductive carbon material was produced as follows. A carbon rod(conductive carbon material) was immersed in 97% sulfuric acid, whichwas heated to 210° C., for 3 hours. The carbon rod was made of graphitehaving a diameter of 6 mm. Each end of the carbon rod was rounded. Whensurface bondings (peaks of a 2p-orbital of a sulfur atom) of the carbonrod (conductive carbon material), which had been subjected to surfacetreatment, were analyzed by electron spectroscopy for chemical analysis(ESCA), there were observed a peak of 170.5 eV which represents abonding of C—SO₃—C or C—SO₄—C and a peak of 171.2 eV which represents abonding of C—SO₃H. Accordingly, a sulfo group was considered to beintroduced into a surface of the conductive carbon material. Thecurrent-voltage properties of the carbon rod that had been subjected tosurface treatment of immersing the carbon rod in a chemical liquid weremeasured under conditions similar to the above example. The distancebetween the carbon rod and the platinum plate was set to be 15 μm.

Further, the current-voltage properties were measured in a mannersimilar to the above example for a comparative experiment in which acarbon rod before immersion in heated sulfuric acid to introduce a sulfogroup was used as an anode, and a platinum plate was used as a cathode.

FIG. 12 shows results of the above experiments. It can be seen from FIG.12 that the carbon rod into which a sulfo group was introduced byimmersion in sulfuric acid had increased current by six or more times ascompared to the carbon rod into which the sulfo group was notintroduced.

The carbon rod into which a sulfo group was introduced by immersion insulfuric acid was used as a processing electrode to perform anelectrolytic process of a copper film formed on a silicon substrate. Theelectrolytic process was conducted at a voltage of 40 V and a current of0.087 mA for 30 seconds while the distance between electrodes was 25 μm.As a result of the electrolytic process, the maximum processed depth was144 nm. At that time, the current efficiency was about 47%. The maximumprocessed depth and the current efficiency were obviously larger thanthose in the aforementioned comparative experiment.

Thus, it can be seen that when the carbon rod into which a sulfo groupwas introduced by immersion in sulfuric acid had increased currentduring the electrolytic process and increased current efficiency ascompared to the carbon rod into which the sulfo group was notintroduced.

FIG. 13 is a schematic diagram showing an electrolytic processingapparatus using such an electrode. As shown in FIG. 13, the electrolyticprocessing apparatus has a pair of electrodes 301 and 302 connected toan anode and a cathode of a power supply 303. The electrodes 301 and 302are made of a graphite intercalation compound containing alkali metal. Afluid 305 such as pure water or ultrapure water is supplied between theelectrodes (graphite intercalation compounds) 301, 302 and a workpiece304 (e.g., a copper film formed on a substrate). Then, the workpiece 304is brought close to the electrodes 301, 302. A voltage is appliedbetween the electrodes 301 and 302 by the power supply 303. Watermolecules in the fluid 305 are dissociated into hydroxide ions andhydrogen ions by the electrodes 301 and 302 made of a graphiteintercalation compound. For example, the produced hydroxide ions aresupplied to a surface of the workpiece 304. The concentration of thehydroxide ions is thus increased near the workpiece 304, and atoms inthe workpiece 304 and the hydroxide ions are reacted with each other toperform removal of a surface layer of the workpiece 304.

Thus, it is possible to reduce the distance between the electrodes 301,302 and the workpiece (substrate) 304 and hence the distance between theelectrode 301 serving as an anode and the electrode 302 serving as acathode. Therefore, the electrolytic processing apparatus can flexiblycope with small electrodes and various shapes of electrodes.Furthermore, because the electrode 301 serving as an anode and theelectrode 302 serving as a cathode have catalysis, a leakage current canbe prevented from being produced between the cathode and the anode,i.e., between the electrodes 301 and 302.

Such an electrode, which includes a graphite intercalation compoundcontaining alkali metal, can be used in an electrolytic processingapparatus of the above embodiments shown in FIGS. 5 through 7, insteadof an electrode in which an organic compound is chemically bonded to asurface of a conductive material.

Methods of synthesizing a graphite intercalation compound include agaseous phase constant-pressure reaction method, a liquid phase contactreaction method, a solid phase pressurizing method, and a solventmethod. The gaseous phase constant-pressure reaction method comprisesdisposing alkali metal and graphite at different positions in a glasstube, sealing the glass tube under a vacuum, and heating the graphiteand the alkali metal while controlling the temperatures thereof Thepositions into which the alkali metal is intercalated and the amount ofthe alkali metal intercalated can be adjusted by controlling thetemperatures of the alkali metal and the graphite. For example, whenpotassium is intercalated into HOPG, the temperatures are set at about250° C. The liquid phase contact reaction method comprises directlycontacting a compound containing alkali in a liquid phase with graphiteto react with each other. The solid phase pressurizing method comprisescontacting alkali metal with graphite, pressurizing the graphite toabout 5 to about 20 atmospheres (about 0.5 to about 2 MPa), and heatingthe graphite to about 200° C. The solvent method comprises dissolvingalkali metal in a solvent such as an ammonium solvent, and immersinggraphite in the solvent.

According to the liquid phase contact reaction method, an electrode madeof a graphite intercalation compound containing alkali metal wasproduced (synthesized) as follows. Sodium nitrate, which has a meltingpoint of 308° C., was heated and melted in a crucible by a burner. Agraphite plate, which had a length of 12.5 mm, a width of 34 mm, and athickness of 0.5 mm, was immersed in the melted sodium nitrate andheated therein for 2 to 3 minutes. Then, the graphite plate was removedfrom the crucible and cooled in air. Thus, an electrode made of agraphite intercalation compound having sodium intercalated betweenlayers of the graphite was produced. Then, the current-voltageproperties were measured in an experimental device as shown in FIG. 14.The experimental device had an acrylic container 320, and a pair ofparallel plate electrodes 321 and 322. The electrode made of a graphiteintercalation compound was used as the electrode 321, and a platinumplate was used as the electrode 322. These electrodes 321 and 322 wereconnected to an anode and a cathode of a power supply 323, respectively.The current-voltage properties were measured in ultrapure water 325,which had a resistivity of 18.2 MΩ·cm. At that time, the distancebetween the electrodes 321 and 322 was set to be 12 μm, and areas of theelectrodes 321 and 322 facing each other were set to be about 0.4 cm².

Further, the current-voltage properties were measured in a mannersimilar to the above for a comparative experiment in which a graphiteplate in which sodium was not intercalated between layers of thegraphite was used as the electrode.

FIG. 15 shows results of the above experiments. It can be seen from FIG.15 that the electrode made of a graphite intercalation compound havingsodium intercalated between layers of the graphite supplied a currentslight lower than 50 mA (a current density of 125 mA m²) at 150 V andthus had increased current by about 50 times as compared to the graphiteplate in which sodium was not intercalated between layers of thegraphite. Therefore, the graphite intercalation compound having sodiumintercalated between layers of the graphite is considered to be capableof promoting to dissociate ultrapure water into hydrogen ions orhydroxide ions.

In the above example, graphite was immersed in a liquid in which sodiumnitrate was heated and melted. However, the graphite may be immersed inany salts containing alkali metal, such as potassium nitrate.

A dilute chemical liquid may be added as an additive to pure water. Forexample, 2-propanol (IPA) may be added to pure water to adjust thepolarity of the pure water.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

1. An electrode for electrolytic processing, said electrode comprising:a conductive material; and an organic compound having an ion exchangegroup, said organic compound being chemically bonded to a surface ofsaid conductive material.
 2. The electrode according to claim 1, whereinsaid organic compound comprises an organic compound selected from thegroup consisting of thiol and disulfide.
 3. The electrode according toclaim 1, wherein said ion exchange group comprises at least one of ionexchange groups selected from the group consisting of a sulfo group, acarboxyl group, a quaternary ammonium group, and an amino group.
 4. Theelectrode according to claim 1, wherein said conductive materialincludes at least one of gold, silver, platinum, copper, galliumarsenide, cadmium sulfide, and indium oxide (III).
 5. An electrode forelectrolytic processing, said electrode comprising: a conductive carbonmaterial; and an ionic dissociation functional group chemicallymodifying a surface of said conductive carbon material.
 6. The electrodeaccording to claim 5, wherein said ionic dissociation functional groupcomprises a sulfo group or a carboxyl group.
 7. The electrode accordingto claim 5, wherein said ionic dissociation functional group comprisesat least one of ion exchange groups selected from the group consistingof a quaternary ammonium group, and a tertiary or lower amino group. 8.The electrode according to claim 5, wherein said conductive carbonmaterial comprises a conductive carbon material selected from the groupconsisting of glassy carbon, fullerene, and carbon nanotubes.
 9. Anelectrode for electrolytic processing, said electrode comprising agraphite intercalation compound containing alkali metal.
 10. Anelectrolytic processing apparatus comprising: a processing electrode; afeeding electrode to feed a workpiece; a workpiece holder for holdingthe workpiece and bringing the workpiece into contact with or close tosaid processing electrode; a power supply for applying a voltage betweensaid processing electrode and said feeding electrode, and a fluid supplyunit for supplying a fluid between the workpiece and said processingelectrode, wherein at least one of said processing electrode and saidfeeding electrode comprises the electrode according to claim
 1. 11. Anelectrolytic processing method, comprising: feeding a workpiece througha feeding electrode; applying a voltage between the feeding electrodeand a processing electrode; supplying a fluid between the workpiece andthe processing electrode; and bringing the workpiece into contact withor close to the processing electrode, wherein at least one of theprocessing electrode and the feeding electrode comprises the electrodeaccording to claim
 1. 12. A method of promoting dissociation of liquidinto ions by a conductive material to which an organic compound havingan ion exchange group is chemically bonded.
 13. The method according toclaim 12, wherein the organic compound comprises an organic compoundselected from the group consisting of thiol and disulfide.
 14. Themethod according to claim 12, wherein the ion exchange group comprisesat least one of ion exchange groups selected from the group consistingof a sulfo group, a carboxyl group, a quaternary ammonium group, and anamino group.
 15. The method according to claim 12, wherein theconductive material comprises a material including at least one of gold,silver, platinum, copper, gallium arsenide, cadmium sulfide, and indiumoxide (III).
 16. An electrolytic processing apparatus comprising: aprocessing electrode; a feeding electrode to feed a workpiece; aworkpiece holder for holding the workpiece and bringing the workpieceinto contact with or close to said processing electrode; a power supplyfor applying a voltage between said processing electrode and saidfeeding electrode, and a fluid supply unit for supplying a fluid betweenthe workpiece and said processing electrode, wherein at least one ofsaid processing electrode and said feeding electrode comprises theelectrode according to claim
 5. 17. An electrolytic processing apparatuscomprising: a processing electrode; a feeding electrode to feed aworkpiece; a workpiece holder for holding the workpiece and bringing theworkpiece into contact with or close to said processing electrode; apower supply for applying a voltage between said processing electrodeand said feeding electrode, and a fluid supply unit for supplying afluid between the workpiece and said processing electrode, wherein atleast one of said processing electrode and said feeding electrodecomprises the electrode according to claim
 9. 18. An electrolyticprocessing method, comprising: feeding a workpiece through a feedingelectrode; applying a voltage between the feeding electrode and aprocessing electrode; supplying a fluid between the workpiece and theprocessing electrode; and bringing the workpiece into contact with orclose to the processing electrode, wherein at least one of theprocessing electrode and the feeding electrode comprises the electrodeaccording to claim
 5. 19. An electrolytic processing method, comprising:feeding a workpiece through a feeding electrode; applying a voltagebetween the feeding electrode and a processing electrode; supplying afluid between the workpiece and the processing electrode; and bringingthe workpiece into contact with or close to the processing electrode,wherein at least one of the processing electrode and the feedingelectrode comprises the electrode according to claim 9.